Defining unacceptable HLA antigens:

Management of the sensitized pediatric renal transplant candidate

Kidney transplantation is the treatment of choice for patients with ESRD as it is associated with improved patient survival and better quality of life, especially in children. There are several barriers to a successful transplant including organ shortage, anatomic barriers, and immunologic barriers. One of the biggest immunologic barriers that precludes transplantation is sensitization, when patients have antibodies prior to transplantation, resulting in positive crossmatches with donor. 30%-40% of adult patients on the wait list are sensitized. There is a growing number of pediatric patients on the wait list who are sensitized. This poses a unique challenge to the pediatric transplant community. Therefore, attempts to perform desensitization to remove or suppress pathogenic HLA antibodies resulting in acceptable crossmatches, and ultimately a successful transplant, while reducing the risk of acute rejection, are much needed in these children. This review article aims to address the management of such patients both prior to transplantation, with strategies to overcome sensitization, and after transplantation with monitoring for allograft rejection and other complications.

Immunologic Risk Assessment and Approach to Immunosuppression Regimen in Kidney Transplantation

The outcomes of kidney transplantation show a steady improvement with an increasing number of transplantations and decreasing incidence of acute rejection episodes. Successful transplantation begins with a comprehensive immunologic risk assessment and judicious choice of therapeutic agents. In this review, we discuss the trends in transplant immunosuppression practices and outcomes in the United States. We discuss practical testing algorithms for clinical decision making in induction therapy and fine-tuning maintenance immunosuppression. We introduce assessment tools for immune monitoring after transplantation and speculate on future directions in management.

Study rationale, design, and pretransplantation alloantibody status: A first report of Clinical Trials in Organ Transplantation in Children-04 (CTOTC-04) in pediatric heart transplantation

Anti-HLA donor-specific antibodies are associated with worse outcomes after organ transplantation. Among sensitized pediatric heart candidates, requirement for negative donor-specific cytotoxicity crossmatch increases wait times and mortality. However, transplantation with positive crossmatch may increase posttransplantation morbidity and mortality. We address this clinical challenge in a prospective, multicenter, observational cohort study of children listed for heart transplantation (Clinical Trials in Organ Transplantation in Children-04 [CTOTC-04]). Outcomes were compared among sensitized recipients who underwent transplantation with positive crossmatch, nonsensitized recipients, and sensitized recipients without positive crossmatch. Positive crossmatch recipients received antibody removal and augmented immunosuppression, while other recipients received standard immunosuppression with corticosteroid avoidance. This first CTOTC-04 report summarizes study rationale and design and relates pretransplantation sensitization status using solid-phase technology. Risk factors for sensitization were explored. Of 317 screened patients, 290 were enrolled and 240 underwent transplantation. Core laboratory evaluation demonstrated that more than half of patients were anti-HLA sensitized. Greater than 80% of sensitized patients had class I (with or without class II) HLA antibodies, and one-third of sensitized patients had at least 1 HLA antibody with median fluorescence intensity of ≥8000. Logistic regression models demonstrated male sex, weight, congenital heart disease history, prior allograft, and ventricular assist device are independent risk factors for sensitization.

Application and interpretation of histocompatibility data in thoracic (heart and lung) transplantation

PURPOSE OF REVIEW

The purpose of the review is to update our current understanding and utilization of immunogenetic tools in heart and lung transplant.

RECENT FINDINGS

Increasingly, complex patients have been managed perioperatively for heart and lung transplant using a variety of tests and techniques. Recent treatment regimens and listing strategies have exploited recent laboratory advances. However, the better characterization has led to an even more complex description of sensitized heart and lung candidates. Several recent studies have examined antibody strengths and behavior to guide clinical decision-making and examine postoperative outcomes. Finally, non-human leukocyte antigen antibodies have emerged as possible determinants of allograft outcome in heart and lung transplant.

SUMMARY

Heart and lung transplant candidates with preformed and de-novo posttransplant antibodies continue to represent a challenging and high-risk group of patients. Modern immunogenetic techniques have broadened our understanding and have revealed an even more complex relationship between antibodies, allografts, and outcomes.

Translational research in kidney transplantation and the role of patient engagement

Background

Translational research is an evolving discipline that is intended to bridge the gaps between basic science research, clinical research, and implementation in clinical practice. It is a fluid, multidirectional process that requires strong interdisciplinary collaboration to produce research that is relevant to end-users.

Purpose of this review

This review summarizes current perspectives on translational research and outlines its relevance and importance to kidney transplantation research.

Sources of information

Sources of information used for this review include published reports, articles, and research funding websites.

Findings

Tissue typing is used as an in-depth example of how translational research has been applied in the field of kidney transplant medicine, and how it has resulted in successful implementation of diagnostic and management options for sensitized individuals undergoing kidney transplantation. The value of actively involving kidney transplant stakeholders (patients, caregivers, and clinicians) in setting research priorities and determining relevant outcomes for future investigation is also discussed.

Limitations

This is a narrative review of the literature which has been partly influenced by the perspectives and experiences of its authors.

Implications

Translational and patient-oriented research practices should be incorporated into future research endeavours in the field of kidney transplantation in order to create beneficial change in clinical practice and improve patient outcomes.

What was known before

Translational research which engages patients in the investigative process can enhance the likelihood that medical discoveries will have a meaningful impact at the bedside.

What this adds

This article applies current perspectives on translational research and patient engagement to the field of kidney transplantation, illustrating how these approaches have led to significant advancements in the field. It provides further justification for deliberate, targeted efforts to cross-collaborate and incorporate the patient voice into kidney transplant research.

[Ten years' experience in the research of abdominal compartment syndrome (2004-2014)]

Intra-abdominal hypertension and abdominal compartment syndrome are frequent findings among severe surgical ill patients. In spite of the fast diagnostic methods and effective therapeutic procedures the mortality is high. The causing factors lead to increased intra-abdominal pressure and abdominal compartment syndrome. It can be defined as adverse physiologic consequences that occur as a result of an acute increase in the intra-abdominal pressure. The most common causes are retroperitoneal haemorrhage, pancreatitis, bowel obstruction, tense ascites, peritonitis and serious visceral edema due to massive fluid resuscitation. The affected systems are cardiovascular, respiratory, renal, central nervous systems, splanchnic organs, and finally the whole body. The diagnostic method is the intra-abdominal pressure monitoring. The bases of the treatment are adequate fluid resuscitation, non-surgical management and decompression. The authors review the topic including the international and Hungarian references based on their ten years experience.

Human leukocyte antigens and alloimmunization in heart transplantation: an open debate

Considerable advances in heart transplantation outcome have been achieved through the improvement of donor-recipient selection, better organ preservation, lower rates of perioperative mortality and the use of innovative immunosuppressive protocols. Nevertheless, long-term survival is still influenced by late complications. We support the introduction of HLA matching as an additional criterion in the heart allocation. Indeed, allosensitization is an important factor affecting heart transplantation and the presence of anti-HLA antibodies causes an increased risk of antibody-mediated rejection and graft failure. On the other hand, the rate of heart-immunized patients awaiting transplantation is steadily increasing due to the limited availability of organs and an increased use of ventricular assist devices. Significant benefits may result from virtual crossmatch approach that prevents transplantation in the presence of unacceptable donor antigens. A combination of both virtual crossmatch and a tailored desensitization therapy could be a good compromise for a favorable outcome in highly sensitized patients. Here, we discuss the unresolved issue on the clinical immunology of heart transplantation.

Impact of donor-specific antibodies in reconstructive transplantation

For many devastating injuries and tissue defects where conventional reconstruction is not possible, reconstructive transplantation such as hand and face transplantation has become a viable alternative. This novel approach allows for improved restoration of appearance, anatomy and function not feasible by other available treatment options. However, clinical management of these injuries prior to transplantation frequently requires multiple blood transfusion or skin grafts resulting in the formation of alloantibodies (anti-HLA IgG Abs) and a high degree of sensitization. The role of donor-specific antibodies (DSA) and mechanisms of antibody-mediated rejection (AMR) in reconstructive transplantation are still largely unknown. Thus there is an imminent need to develop a better understanding of the mechanisms related to DSA and AMR after reconstructive transplantation. In this review, we will define the role of DSA and mechanisms of AMR in reconstructive transplantation and compare them to established measures and treatment concepts in solid organ transplantation.

Transplanting the highly sensitized patient: trials and tribulations

PURPOSE OF REVIEW

Humoral sensitization to antigens of the human leukocyte antigen and ABO systems remains one of the largest barriers to further expansion in renal transplantation. This barrier translates into prolonged waiting time and a greater likelihood of death. The number of highly sensitized patients on the renal transplant waiting list continues to increase. This review focuses on the options available to these patients and speculates on future directions for incompatible transplantation.

RECENT FINDINGS

Desensitization protocols (to remove antibodies), kidney-paired donation (to circumvent antibodies) or a hybrid technique involving a combination of both have broadened the access to transplantation for patients disadvantaged by immunologic barriers. However, the risk of antibody-mediated rejection may be increased and warrants caution. Technical advances in antibody characterization using sensitive bead immunoassays and the C1q assay and therapeutic modalities such as complement inhibitors and proteasome inhibitors have been used to avoid or confront these antibody incompatibilities.

SUMMARY

A growing body of knowledge and literature indicates that these diagnostic and therapeutic modalities can facilitate a safer and more successful treatment course for these difficult-to-treat patients. Rigorous investigations into newer interventions will help in broadening the options for these patients and also expand the living donor pool.

Infusion of high-dose intravenous immunoglobulin fails to lower the strength of human leukocyte antigen antibodies in highly sensitized patients

BACKGROUND

Human leukocyte antigen (HLA) sensitization presents a major obstacle for patients awaiting renal transplantation. HLA antibody reduction and favorable transplantation rates have been reported after treatment with high-dose intravenous immunoglobulin (IVIg).

METHODS

We enrolled 27 patients whose median flow cytometric calculated panel reactive antibody (CPRA) was 100% and mean wait-list time exceeded 4 years in a protocol whereby high-dose IVIg was administered, HLA antibody profiles of sera obtained before and after treatment were characterized, and cross-match tests were performed with all blood group identical kidney offers.

RESULTS

Whereas 12.8% of a similarly sensitized historic control cohort underwent transplantation in the course of a year, 41% of the IVIg-treated group underwent transplantation during the study period. Surprisingly, HLA antibody profiles, measured by CPRA, showed no significant change in response to IVIg treatment. In fact, retrospective cross-match testing using pretreatment sera of those receiving deceased-donor allografts showed that all patients would have been eligible for transplantation with their respective donors before IVIg infusions.

CONCLUSIONS

This study does not corroborate previous reports of CPRA reduction leading to increased deceased-donor transplantation rates in broadly sensitized patients undergoing desensitization with high-dose IVIg. The increased rate of transplantation relative to historic controls is not related to improved cross-match eligibility and likely resulted from frequent crossmatching using a cytotoxic strength threshold, improved medical readiness for transplantation, and newly recognized options for live-donor transplantation, all of which could have been achieved without IVIg treatment.

Luminex and antibody detection in kidney transplantation

Preformed anti-human leukocyte antigen (HLA) antibodies have a negative effect on kidney transplantation outcome with an increased rejection rate and reduction in survival. Posttransplantation production of donor-specific anti-HLA antibodies is indicative of an active immune response and risk of transplantation rejection. For many years the primary technique for anti-HLA antibody detection was complement-dependent cytotoxicity (CDC), which has been integrated by solid-phase assays as HLA antigen-coated bead methods (Luminex). This new technological approach has allowed identification of anti-HLA antibodies, not detectable using conventional CDC method, in patients awaiting kidney transplantation. Moreover, use of Luminex technology has enabled better definition of acceptable or unacceptable antigens favoring transplantation in highly immunized patients. However, there are still many unresolved issues, including the clinical relevance of antibodies detected with this system.

Application of calculated panel reactive antibody using HLA frequencies in Koreans

Background

Introduction of the Luminex panel reactive antibody (PRA)-single antigen (SA) assay has increased the detection rates of unacceptable antigens in sensitized patients; the calculated PRA (CPRA) level represents the percentage of actual organ donors that express 1 or more of these unacceptable antigens. We developed a CPRA calculator based on the HLA frequencies in Koreans to measure sensitization levels in Korean patients.

Methods

To develop the calculator, we obtained the HLA-A, HLA-B, and HLA-DR phenotypes of 1,622 Koreans, and compared these with previously reported frequencies in Koreans. Sera from patients awaiting kidney transplantation were tested for HLA antibodies by Luminex PRA-screen, PRA-identification (ID), and PRA-SA assays. The measured %PRA from the PRA-screen (N=55) and PRA-ID (N=71) were compared to the %CPRA for the unacceptable antigens obtained from PRA-SA.

Results

Phenotype frequencies used for the CPRA calculator agreed with previously reported data. The concordance rates among the 3 PRA methods for the detection of class I and class II antibodies were 76.1-81.8% (kappa, 0.519-0.636) and 72.7-83.6% (0.463-0.650), respectively. For the detection of broadly sensitized sera (>50% or >80%), the concordance rates were over 80%. In sera with 80-100% CPRA, 91.7% and 94.4% of the samples had concordant results (80-100% PRA) in the PRA-screen and PRA-ID assay, respectively.

Conclusions

Although further clinical studies are required to confirm the benefits of CPRA values, adoption of CPRA analysis based on HLA frequencies in Koreans may be useful for sensitization measurements and organ-allocation algorithms.

Mastering the risk of HLA antibodies in kidney transplantation: an algorithm based on pretransplant single-antigen flow bead techniques

The utilization of sensitive techniques of detection of HLA antibodies to define and measure sensitization has greatly evolved in recent years. We present here an approach to minimize the risk of HLA antibodies in kidney transplantation based on the evaluation of graft accessibility of sensitized patients by calculated PRA (cPRA) and estimation of potential matched donors (PMD) using a national simulation software program. This study included all registered patients on our waiting list (WL) for deceased donor (DD) kidney transplants. All patients were screened by single-antigen flow bead (SAFB) techniques. Of the 502 registered patients, 174 (34.7%) were sensitized. Among these, 48.3% (84 pts) had a cPRA>85%. For 75.3% of sensitized patients (90 pts with cPRA≤85% and 41 pts with cPRA>85%), the flow of PMD was considered sufficient to allow a transplant avoiding all unacceptable antigens. The 41 patients with a cPRA>85% (48.8%) had a satisfactory donor flow in the framework of the national prioritization program for highly sensitized patients. Finally, 43 sensitized patients (24.7%) were deemed eligible for a strategy of higher immunological risk through desensitization protocols or transplantation against HLA-DSAs. This approach provides a logical and systematic strategy to rationalize the access of sensitized patients to kidney transplantation minimizing the risk of HLA antibodies.

The complexity of human leukocyte antigen (HLA)-DQ antibodies and its effect on virtual crossmatching

BACKGROUND

We previously reported that in patients possessing human leukocyte antigen (HLA)-DQ-directed antibodies, the target molecule may include the patient's own DQβ chain if it is paired with non-self-DQα chain, thus forming a different DQ target. Herein, we sought to assess the breadth of this phenomenon.

METHODS

Serum samples from 104 patients awaiting kidney transplantation, known to have DQ antibodies, were studied. Antibody identification was performed using luminex-based HLA class II single-antigen bead assays from two vendors; DQA1/DQB1 typing was performed using luminex polymerase chain reaction - sequence specific oligo prob hybridization (PCR-SSO) technology.

RESULTS

A total of 71% of the 104 serum samples studied contained antibodies reactive against test beads coated with the patient's own DQα- or β-chain components. Of those, 35 patients (34%) exhibited antibodies to their own DQβ chain when in combination with non-self-DQα chains; and 64 patients (62%) had antibodies to their own DQα chain when in combination with non-self-DQβ chains. This is a striking observation.

CONCLUSIONS

To the best of our knowledge, this is the first systematic, high-resolution evaluation of DQ antibody repertoire. With the expansion of virtual crossmatching, particularly in the context of a national registry, the need for more detailed DQ antibody or antigen evaluation is critical to improve operational efficiency and patient outcomes.

Calculated PRA: initial results show benefits for sensitized patients and a reduction in positive crossmatches

The calculated panel reactive antibody (CPRA), which is based upon unacceptable HLA antigens listed on the waitlist form for renal transplant candidates, replaced PRA as the measure of sensitization among US renal transplant candidates on October 1, 2009. An analysis of the impact of this change 6 months after its implementation shows an 83% reduction in the number of kidney offers declined nationwide because of a positive crossmatch. The increasing acceptance and utilization of unacceptable HLA antigens to avoid offers of predictably crossmatch-positive donor kidneys has increased the efficiency of kidney allocation, resulting in a significant increase in the percentage of transplants to broadly sensitized (80+% PRA/CPRA) patients from 7.3% during the period 07/01/2001-6/30/2002 to 15.8% of transplants between 10/1/09-3/31/10. The transplant rates per 1000 active patient-years on the waitlist also increased significantly for broadly sensitized patients after October 1, 2009. These preliminary results suggest that 'virtual' positive crossmatch prediction based on contemporary tools for identifying antibodies directed against HLA antigens is effective, increases allocation efficiency and improves access to transplants for sensitized patients awaiting kidney transplantation.

Long-term outcome of highly sensitized African American patients transplanted with deceased donor kidneys

Undertaking transplantation in highly sensitized African American (AA) patients as transplant recipients represents a unique challenge. We retrospectively compared the outcomes of AA with non-African American (NAA) patients who had panel reactive antibody >80% and received deceased donor (DD) kidneys by virtual crossmatch. Immunosuppressive regimen included basiliximab induction and tacrolimus, mycophenolate acid and steroids maintenance. Among 835 consecutive transplants from 1998 to 2007, 142 (17%) were sensitized patients including 89 (16.6%) AA and 53 (17.7%) NAA patients. The AA group had similar 5-year incidence of acute rejection as NAA group (21.4% vs. 26.4%, P = 0.25). Kaplan-Meier estimated graft survival at 1, 3 and 5 years were 91%, 85% and 82% in AA group, and 94%, 79% and 71% in NAA group (P = 0.08). The death-censored graft survival at 1, 3, and 5 years were 93%, 86% and 84% in AA group, and 96%, 83% and 78% in NAA group (P = 0.11). The 1, 3, and 5 years patient survivals were 93%, 88% and 85% in AA group, and 96%, 96% and 94% in NAA group (P = 0.17). Highly sensitized AA patients could be transplanted with DD kidneys at a similar rate as NAA patients, and they may not have a higher incidence of rejection or an inferior graft survival than NAA patients.

Calculated PRA (CPRA): the new measure of sensitization for transplant candidates

The ways we measure whether a patient is sensitized to HLA antigens and to what extent sensitization affects access to transplantation have changed remarkably during the past decade. What we mean by sensitized and broadly sensitized today is heavily dependent upon the sensitivity of the test that is used to measure antibodies. Because we provide additional allocation points for broadly sensitized patients in the United States kidney allocation system in an effort to compensate for their biological disadvantage, some consistency and accountability are required. The calculated panel-reactive antibody, which provides an estimate of the percentage of deceased organ donors that will be crossmatch incompatible for a candidate provides both consistency and accountability.

Emerging role of donor-specific anti-human leukocyte antigen antibody determination for clinical management after solid organ transplantation

Preformed and de novo donor-specific HLA antibodies (DSA) have been associated with allograft dysfunction and failure. The application of solid-phase methods have increased the sensitivity and specificity of antibody detection; however the clinical significance of these DSA is under evaluation. In the present study, we summarize six cases (four renal transplant recipients, one multivisceral recipient, and one heart-and-lung transplant recipient) to illustrate the role of the histocompatibility laboratory in providing the most comprehensive workup to assess the risk of graft dysfunction associated with antibody-mediated rejection (AMR). These cases illustrate the potential risk assessment for AMR in various situations: (1) in patients exhibiting low levels of DSA pretransplantation; (2) protocol immunosuppression minimization during stepwise weaning; and (3) desensitization protocols. Furthermore, increased sensitivity of DSA determination is indicated for the interpretation of focal C4d and its clinical significance. The clinical relevance of monitoring for circulating DSA with solid-phase single-antigen assays is also discussed. These cases exemplify the rationale for all patients to be monitored for DSA post-transplantation, with the frequency adjusted based on the individual risk for AMR.

Naturally occurring interference in Luminex assays for HLA-specific antibodies: characteristics and resolution

Substances occurring naturally in the sera of patients can interfere with Luminex antibody assays, causing increased background and changes in antibody specificity. We present data on the effectiveness of hypotonic dialysis (HD) or dithiothreitol (DTT) treatment in eliminating this interference. HD significantly increased reaction strength of positive control beads and reduced reaction strength of negative control beads. HD also improved specificity identification, determination of donor-specific antibody (DSA) strength, and crossmatch predictability compared with values in untreated serum. DTT also increased the reaction strength of positive control beads, but in most cases, further increased reactivity of negative control beads. DTT improved crossmatch predictability but to a lesser extent than did HD and may differ with specificities defined in other assays. Because interference is frequently observed in sera from highly sensitized patients, it is important to recognize and eliminate interference in Luminex antibody assays for accurate and meaningful test interpretation.

Detecting and monitoring human leukocyte antigen-specific antibodies

Renewed awareness of the relevance of HLA-specific antibodies to transplantation and the development of protocols to reduce or eliminate sensitization have made monitoring of antibodies and accurate interpretation of test results increasingly important. Here we review the various tests available and provide guidelines for the development of monitoring protocols.